Spark advance adjustment device



May 12, 1970 'w. B- CHAMBERS SPARK ADVANCE ADJUSTMENT DEVICE Filed July 2, 1968 m 3 M m 6 0/. 0 z 4 I w 0 3 39 4 5 H M; m g M \l fl il a 7 m Q 45 y n irranvzr;

United States Patent 3,511,945 SPARK ADVANCE ADJUSTMENT DEVICE Willie B. Chambers, Inglewood, Calif., assignor to Eelco Mfg. & Supply Company, a corporation of California Filed July 2, 1968, Ser. No. 742,033 Int. Cl. H01h 19/62 US. Cl. 200-31 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention The field of art to which the invention pertains includes the field of adjustable cam operated periodic circuit makers and breakers.

Description of the prior art In the operation of an internal combustion gasoline engine, rotation of a cam shaft actuates intake and exhaust valves to open and close the intake and exhaust ports leading to the combustion chambers located within the head of the engine. The period of time during which both the intake and exhaust ports are closed is referred to as the duration. Firing of the spark plugs within the combustion chamber to ignite the gasoline must occur during the duration. Further, the spark plug must be fired before the end of the compression stroke since it takes a certain time to complete combustion. The better the fuel quality, the higher the engine speed and the smaller the load, the more the spark plug firing must be advanced.

Spark timing is related to engine speed by means of a centrifugal governor built into the distributor. The distributor encloses a circuit breaker which includes an interruptor cam with as many cam lobes as there are cylinders to be fired. Flyweights on the centrifugal governor move the interrupter cam angularly relative to its shaft. Spark timing is also related to engine load by the intake-manifold vacuum which varies inversely as the load. The vacuum acts on a diaphragm through which breaker contacts, mounted on a base, are angularly rotated.

When increasing the power of an automobile engine, for racing or otherwise, adjustments are often made to keep both the intake ports and exhaust ports open for as long as possible, thereby reducing the duration. Normally, this is done by utilizing a new cam shaft or by regrinding the stock cam shaft in order to obtain the desired opening and closing of the intake and exhaust valves. When this is done, the maximum spark advance generally must be finely adjusted and reset to optimize spark timing at high engine speeds. The initial, mechanical spark advance setting (relative to the end of the compression stroke) is generally about 20. Centrifugal spark advance adds another 20 for a total of 40 spark advance. If, as a result of substitution or regrinding of the cam shaft, a smaller amount of maximum spark advance is desired, then the total spark advance is set 3,511,945 Patented May 12, 1970 by moving the distributor shaft so that the initial or mechanical amount of spark advance is decreased. For example, if a maximum spark advance of 35 is desired, then the distributor shaft must be adjusted so that the mechanical amount of spark advance (i.e., minimum spark advance) is 15. While this allows for the desired optimum performance at high speeds, at low speeds the engine will have decreased power and will be very difiicult to start. Accordingly, it is very desirable to be able to adjust the maximum spark advance without decreasing the initial or mechanical spark advance.

SUMMARY OF THE INVENTION The present invention provides a device that is readily attachable to the distributor structure and which allows the maximum spark advance to be adjusted without affecting the initial, mechanical spark advance setting.

Typically, a centrifugal spark advance mechanism carries a pin which moves in accordance with changes in spark advance and extends through a slot in a support plate for the mechanism. The present invention provides a means for limiting the movement of such pin to achieve a desired maximum spark advance position and which allows adjustment to increase or decrease the maximum spark advance. Specifically, a bracket is provided carrying an adjustment screw which includes a threaded shank and a head which has a substantially greater diameter than the threaded shank. The screw is threaded through upstanding ears on the bracket and the bracket is secured within the distributor structure so that the screw head abuts the aforenoted pin when the pin is in a desired maximum spark advance position. By merely turning the screw head its lateral position with respect to the pin changes to correspondingly change the maximum spark advance position of the pin.

In further embodiments of the invention, means are provided for imparting frictional drag on the screw and comprises a button of resilient material such as a plastic set into the bracket to lie beneath the screw shank. The thickness of the button is sufficiently greater than the distance thereat between the threads on the shank and the surface of the bracket to provide frictional drag when the threaded shank is passed thereover.

In other embodiments, the bracket is arcuately shaped to form a semicircle and has symmetrically disposed pairs of upstanding ears at each end with symmetrically disposed holes between the ears of each pair to receive the aforementioned plastic button. The adjustment screw extends between the ears of one of such pair and is readily removable therefrom to extend between the ears of the other pair; in this manner the bracket is universal in that it can be mounted upon any distributor mechanism presently in existence. The bracket is attached to the support plate of the centrifugal mechanism by means of holes disposed therein in correspondence to holes in the support plate through which the support plate is normally attached to the rotor of the distributor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a distributor structure utilizing a bracket of this invention, shown with the rotor and interruptor cam extended from the breaker plate structure portions of the distributor;

FIG. 2 is a detailed perspective view of the rotor of FIG. 1 turned from the position shown in FIG. 1 and with associated interruptor cam and adjustment bracket;

FIG. 3 is an elevational view of an adjustment bracket of this invention taken on line 3-3 of FIG. 2, in the direction of the arrows; and

FIG. 4 is a sectional view looking down on the rotor cap of FIG. 2, and sectionalized to illustrate details of the centrifugal spark advance mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a distributor is shown having a 5 bottom or base plate 12 which includes an elongated bearing member 14 in which a distributor shaft 16 is journaled. A breaker plate '18 is journaled around a bearing 20 formed by an upturned collar on the base 12. The breaker plate 18 has an upturned flange or collar 22 centrally located thereof which fits over the bearing 20 whereby the breaker plate 18 is rotatably journaled around the distributor shaft 16. A cam 24 is positioned adjacent the upper end of the distributor shaft 16, which cam carries a centrifugal weight support plate 26 (FIG. 2) at its upper end which plate is immovably attached thereto. The view in FIG. 1 is partially exploded in that the rotor 28 of the distributor and associated cam 24 and distributor shaft 16 are shown extended from the remaining structure of the distributor 10. In normal position, the cam 24 is held astride the upturned flange 22 of the breaker plate 18 supported on the upper edge of the bearing 20. The cam 24 is an interruptor cam in that it is provided with a plurality of cam lobes 30 which successively engage a cam follower on a set of points in the form of the rubbing block 32, a circuit breaker lever 34 to open and close cooperable contacts 36 and 38 carried by the lever 34 and a bracket 40, respectively.

Referring to FIG. 2, the interrupter cam 24 carries the centrifugal weight support plate 24 on an extension 44 of its upper end and is immovably attached thereto. The support plate 26 is apertured in the center thereof so that the distributor shaft 16 may pass therethrough. Referring also to FIG. 4, the upper end of the distributor shaft 16 carries a wing-shaped plate 46, which plate 46 is fixedly mounted on the distributor shaft 16. The support plate 26, together with its attached cam 24, are movable relative to the distributor shaft 16 and wing-shaped plate 46 through a predetermined degree of rotatable motion. The support plate 26 has a pair of centrifugal weights 48 and 50 pivotally mounted thereon, which weights are attached by means of springs 52 and 54, adjacent their outer extremities, to the wing-shaped plate 46 at its outer extremities. As the distributor shaft rotates (in the direction of the arrow 56), it drives the attached wing-shaped plate 46, the support plate 26 and the interrupter cam 24. However, as the speed increases, the pivoted weights 48 and 50 are centrifugally thrown outwardly so as to adjust the cam advance with respect to the distributor shaft 16 whereby the timing is automatically advanced in response to the speed of the engine through a predetermined range. When the pivoted weights 48 and 50 are thrown outwardly, eccentrically disposed end portions 49 and 51 thereof, respectively, rotate the wing-shaped plate 46 to obtain the aforenoted cam advance. A pin 53 (see also FIG. 3) is attached to the wing-shaped plate 46 on one side of the distributor shaft and extends through a slot 55 in the support plate 26. Since the pin 53 is carried by the centrifugal mechanism, it moves in accordance with changes in spark advance and is limited in movement by the dimensions of the support plate slot 55. In this particular case, movement of the pin 53 from its initial setting to its maximum spark advance position, as limited by the support plate slot 55, corresponds to a spark advance change of about 20.

A vacuum responsive diaphragm device 57 is shown in FIG. 1 which is connected to the intake-manifold to angularly displace the breaker plate 18. Angular displacement is in response to intake-manifold vacuum, which varies inversely as the load on the engine. The result is additional spark advance under small engine loads.

The centrifugal mechanism is covered by a rotor 28 which is formed from a suitable insulating material such as Bakelite and which is attached to the support plate 26 by means of screw through holes located in recessed portions 58 in the rotor 28. The rotor 28 includes a spring contact 60 which is electrically connected to a rotor terminal member 62. This spring contact 60 engages a central terminal in the distributor cap (not shown) so that when the rotor 28 is turned by the distributor shaft 16, the rotor terminal member 62 progressively passes adjacent various terminals in the cap to thereby distribute current to the spark plugs.

The foregoing described distributor structure is wellknown to the art and further description thereof can be found in US. Pat. No. 2,769,047 to H. L. Hartzell, D. C. Redick and C. L. Julian.

As noted, a pin 53 is supported by the centrifugal spark advance mechanism and extends through a slot 55 in the support plate 26. Referring to FIG. 3, in conjunction with FIGS. 2 and 4, a bracket 64 of this invention is shown having a generally arcuate, semicircular shape and which is disposed on the support plate 26. The bracket 64 has a pair of upstanding cars 66 and 68 adjacent one end thereof and a symmetrically disposed identical pair of upstanding ears 70 and 72 adjacent the opposite end thereof. Both pair of ears serve the same purpose, which purpose will be further detailed below, but only one pair of ears is utilized with any distributor. By providing an oppositely disposed pair of cars, the bracket is made universal and usable with distributors having their parts in reverse order from the order here illustrated. For simplicity of explanation, reference will generally be made only to that symmetrical half of the bracket directly utilized in the device here illustrated.

Each of the upstanding ears 66 and 68 have openings therein, at 74 and 76, respectively, which are threaded to threadably receive the threaded shank 78 of a screw 80. The screw 80 has a head 82 thereon with a notch 84 therein to provide ready access for a screwdriver. The head 82 has a flattened inner surface 86 which has a substantially greater diameter than the diameter of the threaded shank 78. The bracket 64 is secured to the support plate 26 so that the flat inner surface 86 of the head 82 abuts the pin 53 extending through the support plate slot 55 when such pin 53 is in a desired maximum spark advance position.

The relationship between the screw head 82 and the pin 53 is shown more clearly in FIG. 3 than in the other figures. At slow engine speeds when the centrifugal weights 4-8 and 50 have not been extended, the pin 53 is in its initial or mechanical setting, at the right side (in FIG. 3) of the slot 55 in the support plate 26. As the speed of the engine increases the centrifugal weights 48 and 50 swing out to thereby rotate the wing-shaped plate 46 and move the pin 53 in the direction of the arrow 88. By securing the bracket 64 so that the flat inner surface 86 of the screw head 82 lies in the travel path of the pin 53, movement of the pin 53 toward the left can be stopped at any point up to the left edge of the support plate slot 55. By limiting movement to the left of the pin 53, one effectively limits spark advance increase. The position of the flat inner surface 86 of the head 82 thus determines the desired maximum spark advance position. If the full centrifugal advance is desired, the screw head 82 may merely be threaded out of the upstanding ears 66 and 68 to lie outside of the area above the support plate slot 55. To decrease maximum spark advance one need merely thread the screw 80 into the upstanding ears 66 and 68 until the flat inner surface 86 of the head 82 is at the desired maximum spark advance position. It will be seen that none of these adjustments result in a change in the initial or mechanical spark advance position so that the undesirable consequences previously experienced with prior methods of limiting maximum spark advance are completely alleviated.

Referring to specific details of construction of the bracket 64, friction-imparting means are provided to restrain movement of the screw shank 78. A hole 90 is provided in the bracket 64 between the ears 66 and 68 and underlying the screw shank 78. A button 92 of resilient material such as Teflon or nylon or other such plastic is set in the hole 90. The button 92 has a thickness sufiiciently greater than the distance between the surface of the bracket 64 thereat and the bottom of the threaded shank 78 so as to provide frictional drag on the screw 80 when the threaded shank 78 is passed thereover. By such means, a secure setting is obtained which resists vibrational disturbances. A similarly disposed hole 94 is provided on the opposite end of the bracket between the other pair of ears 70 and 72.

Securing holes, at 96 and 98, are provided in the bracket for attachment thereat to the support plate 26. The sup port plate 26 is connected to the rotor 28 at the recessed portions 58 of the rotor 28 as previously indicated and holes in the support plate 26 are provided for this purpose. These holes are utilized to secure the bracket 64 to the support plate 26; by so doing, installation of the bracket is simple and inexpensive, requiring only bolts 100, lock washers 102 and nuts 104 for each hole 96 and 98. v

To install the bracket 64, one need merely remove the screws holding the rotor 28 to the support plate 26, insert the resilient button 92 in the appropriate hole 90 therefor (although it is contemplated that an extra button can be provided preset in the symmetrically disposed hole on the opposite end of the bracket), position the bracket 64 so that its securing holes 96 and 98 overlie the corresponding holes in the support plate 26, and bolt the bracket 64 thereat to the support plate 26 and rotor 28 with the bolts, lock washers and nuts previously described. The adjustment screw 80 can then be inserted with the fiat inner surface 86 of its head 82 positioned to limit movement of the pin 53 to a desired maximum spark advance position.

What is claimed is:

I1. An adjustment device for limiting the spark advance of a centrifugal spark advance distributor mechanism in which a pin carried by said mechanism and moving in accordance with changes in spark advance as determined by the rotational speed of a distributor shaft, extends through a slot in a support plate therefor, comprising:

a bracket with ends thereof disposed on opposite sides of said shaft;

a first ear adjacent one end of said bracket defining a threaded opening therethrough;

a second ear adjacent the opposite end of said bracket defining a threaded opening therethrough;

an adjustment screw including a threaded shank, adapted to be threaded through one or the other of said ears, and a head having a substantially greater diameter than said threaded shank; and

means for securing said bracket with said screw head abutting said pin when said pin is in a desired maximum spark advance position.

2. The adjustment device of claim !1 including an additional ear on each side of said bracket disposed in confronting relation with said respective first or second ear and each defining an opening therethrough on a common axis with the opening in said respective first or second ear, said additional ears being adapted to receive said shank therethrough, said shank extending from said first or second ear to the additional ear thereat.

3. The adjustment device of claim 1 including means for imparting frictional drag on said screw.

4. The adjustment device of claim 1 including a button of resilient material set in said bracket to lie beneath said screw shank when said screw is threaded through said ear and extending from the surface of said bracket a distance sufi'iciently greater than the distance thereat between the threads on said shank and the surface of said bracket to provide frictional drag on said screw when said threaded shank is passed thereover.

5. The adjustment device of claim 1 in which said support plate defines holes for attachment thereat to a rotor of said distributor, wherein said bracket has a portion normal to each of said first and second ears, abutting said plate and defining a hole, said portions being shaped so that said holes therein overlie said support plate holes for attachment of said bracket thereat.

6. The adjustment device of claim 1 in which said support plate defines two holes disposed on opposite sides of said distributor shaft for attachment at said support plate holes to a rotor of said distributor, wherein said bracket arcuately extends from one of said support plate holes to the other of said support plate holes and defines a hole at each arcuate end thereof overlying a support plate hole at that end for attachment of said bracket thereat.

7. The adjustment device of claim 1 wherein said bracket is arcuately shaped to form a semicircle.

8. The adjustment device of claim 7 wherein said bracket defines a hole adjacent each ear to lie beneath said screw shank and adapted to receive a button of resilient material therethrough for imposing frictional drag on said shank when said shank is extended over said button.

9. The adjustment device of claim 1 wherein said bracket is arcuately shaped to form a semicircle and has a first pair of confronting upstanding ears at one end thereof, including said first ear, and a second pair of confronting upstanding ears, including said second car, symmetrical With said first pair of ears and disposed at the opposite end of said bracket, the ear of each of said pairs opposite said first or second ears defining an opening to receive the shank of said adjustment screw, said shank extending between the ears of said first pair of ears and readily removable for extension between the ears of said second pair of ears.

10. A distributor structure, comprising in combination:

a circuit breaker;

a rotatable shaft;

'a cam carried by said shaft and adapted to actuate said circuit breaker;

a spark advance mechanism carried on said shaft and adapted to rotate said cam within limits with respect to said shaft in accordance with the rotational speed of said shaft;

a pin carried by said spark advance mechanism and moving in accordance with spark advance;

a plate supporting said spark advance mechanism and defining a slot, said pin extending through said slot;

means exterior of said support plate and abutting said pin when said pin is in a desired maximum spark advance position;

means supporting said exterior means in said abutting position on one side of said shaft and adapted to allow adjustment of said abutting position to increase or decrease said maximum spark advance; and

means for supporting said exterior means on the opposite side of said shaft.

References Cited UNITED STATES PATENTS 1,590,772 6/1926 Moore 64-25 2,699,657 1/1955 Vogel 64-25 3,196,224 7/ 1965 Tagliabue 20022 3,430,459 3/1969 Hill 64-25 ROBERT K. SCHAEFER, Primary Examiner J. R. SCOTT, Assistant Examiner US. Cl. X.R. 200l9 

